The subject matter of the present invention relates generally to a high pressure liquid spray cleaning apparatus and method, and in particular to such a cleaning apparatus and method in which the liquid spray is directed at an acute angle between its axis and the surface of the object being cleaned, such angle and the spacing between the spray nozzle and such surface being maintained substantially constant over a given surface area. The pressure of the cleaning liquid at the object surface is also maintained substantially constant over the given area in the range of about 2,000 to 6,000 psi. This results in a tangential shearing action which removes any material coated on the object surface quickly and efficiently.
The cleaning apparatus and method of the present invention are especially useful in cleaning the interior surfaces of container tanks, such as those in which chemical reactions are performed including the polymerization of polyvinyl chloride. However, the cleaning apparatus of the present invention is also useful in cleaning external surfaces of flat or rounded objects, such as removing the paint from ships or bridges. When cleaning container tanks, the cleaning apparatus is automatically moved into and out of an opening in the top of such tanks and the cleaning nozzles are moved over the inner surface of the tanks along a complex predetermined path by means of a motor drive means which may be controlled by an electronic computer. This is important because the container tanks are often provided with baffles, agitator blades and other obstructions inside such tanks which must be cleaned in addition to avoiding striking such obstructions with the spray nozzle when the inner surfaces of the tanks are cleaned. Thus, the spray nozzles must move around such internal obstructions along the predetermined path which requires a very complex motion of such nozzles that is accomplished by the computer in accordance with computer programs stored therein.
Previously, most container tanks are cleaned by manual scraping of the interior surface of such tanks which may scratch the surface and requires a man to enter the tanks so that it may be hazardous, especially if such tanks contain dangerous chemicals or fumes. In addition, manual scraping is extremely time consuming and inefficient to that sometimes not all of the material coating the interior surface is removed. This is extremely important in chemical reactor tanks because any material left coated on their interior surface may result in the contamination of succeeding chemical reactions formed in the tank.
For these reasons, it has previously been proposed to clean the interior surface of the container tanks automatically by liquid spray apparatus, such as that shown in U.S. Pat. RE27,612 of Ruppel et al., granted Apr. 3, 1973. However, in this apparatus, the spray nozzles are raised and lowered within the tank by folding support arms which are pivoted by a manually operated winch connected to such support arms through a wire wound on such winch. In addition, the spray nozzles were rotated about two mutually perpendicular axes so the angle formed between the liquid spray and the object surface changed continuously. Thus, the distance between the spray nozzles and the object surface being cleaned varied and the spray angle was not maintained substantially constant over a given surface area. This change in angle and spacing between the liquid spray and the object surface results in slow and inefficient cleaning so that such automatic cleaning apparatus has not been widely adopted.
To a similar effect is the spray cleaning apparatus of U.S. Pat. No. 3,645,452 of Stoeckel et al., granted Feb. 29, 1972, and in U.S. Pat. No. 3,741,808 of Stalker, granted June 26, 1973, both of which vary the distance and angle between the cleaning liquid spray and the surface of the object being cleaned. However, these apparatus employ telescoping support apparatus or cylinder operated support apparatus for moving the nozzles up and down within the container tank, unlike the folding support arms of U.S. Pat. No. RE27,612.
In addition, it has been previously suggested in U.S. Pat. No. 3,358,935 of Andersen, granted Dec. 19, 1967, to provide a liquid spray cleaning apparatus having spray nozzles mounted on folding support arms which are both manually adjusted into different pivot positions for changing the angle and distance between the spray nozzles and the object surface being cleaned. However, there is no means for automatically pivoting the nozzle support arms in order to maintain the nozzles at substantially the same acute angle and spacing distance to the object surface while such nozzles are moved along a predetermined path in the manner of the present invention.
The above mentioned prior spray cleaning apparatus has been subjected to considerable bending forces on the main support shaft which can cause damage to such shaft or at least deflection of the shaft axis so that inefficient cleaning results. This problem is overcome in the apparatus of the present invention by balancing the reactive forces exerted by the liquid sprays on the nozzles and their support arms so that such reactive forces tend to cancel each other or produce substantially no bending force on the main support shaft in all positions of the nozzle support arms. Thus, while in the folded positions of the support arms the reactive forces do not cancel each other, they produce a total resultant force in a direction substantially coaxial to the main vertical support shaft so that it exerts no bending force on such main support shaft.